Improved methods of making electric discharge device envelopes



. 2, 1958 M. w. EDWARDS ETAL 2,862,336

IMPROVED METHODS OF MAKING ELECTRIC DISCHARGE D vIcE ENVELOPES Filed April 25, 1956 INVENTORSI MARTIN o. MURPHY,

MONTE W. EDWARDS, BY MQWW THEIR ATTORNEY.

United States Patent 2,862,336 IMPROVED METHODS OF MAKING ELECTRIC DISCHARGE DEVICE ENVELOPES Monte W. Edwards and Martin 0. Murphy, Owensboro,

Ky., assignors to General Electric Company, a corporation of New York Application April 25, 1956, Serial No. 580,647 2 Claims. (CI. 49-81) Our invention relates to electric discharge devices and pertains more particularly to new and improved methods for manufacturing electric discharge device envelopes.

Some electric discharge, devices comprise an electrode mount structure sealed in an envelope and including a plurality of electrode elements supported in insulated spaced relation between spaced insulators. Often the envelope is fabricated by sealing a closure member or stem in an open end of a glass bulb or the like. The stem is generally constructed with conductive leads extending therethrough and supporting the electrode mount structure which is positioned in the bulb before sealing and is disposed in the bulb portion of the envelope following sealing of the stem thereto. 1

The mentioned bulbing operation has customarily been accomplished by butt-sealing the open end of the bulb to a planar surface of the stern. Several undesirable effects often result with this type of seal. For example, it has been found that a satisfactory seal generally results when the inner surface of the seal between the bulb and stem is formed as a round fillet flowing smoothly from the bulb portion into the stem portion, and when this is to provide new and improved methods of'manufacturing electric discharge device envelopes.

Another object of the present invention is to provide new and improved methods for reducing the amount of production loss due to failure of seals between bulbs and lead stems.

Another object of the present invention is to'provide new and improved methods for obtaining improved seals adapted for withstanding considerable temperature changes.

Another object of the present invention is to provide new andv improved methods for sealing mount structures in electric discharge devices whereby the assembly of the devices is facilitated and the enveloping operation'is expedited.

Further objects and advantages of our invention will become apparent as the following description proceeds and the features of novelty which characterize our invention will be pointed out with particularity in the claims annexedto and forming part of this specification.

In carrying out the objects of therpresent invention we provide a tube bulb including a flared open end. The

flared end enables the stem to engage the inner surface of the bulb to provide for a desirable type of seal. Subsequent'to such engagement, the bulb end'and stem are heated to a fusion consistency, after which a force is applied between the stem and bulb whereby the-stem and bulb end are fused with an action causing excessmaterial to flow outwardly rather than inwardly toward the stem leads. Thereafter, the stem is rolled whereby the excess material is desirably distributed externally of the bulb.

erence may be had to the accompanying drawing where- 1n:

Figure 1 is an enlarged, perspective, exploded view illustrating certain features of the present invention;

Figure 2 is an enlarged, fragmentary, sectional view illustrating the heating step of the present invention;

Figure 3 is an enlarged, fragmentary, sectional view illustrating another step of the sealing operation; I

Figure 4 is an enlarged, fragmentary, partially sectionalized view illustrating the rolling step in the method of the present invention; and

Figure 5 is an enlarged, fragmentary, partially sectionalized view of a modified form of the present invention.

Referring to Figure 1, there is shown an electric discharge device generally designated 1 and constructed to include a bulb structure 2 formed of a suitably insulative material such as glass. The bulb 2 includes a substantially cylindrical body portion 3, an exhaust tubulation 4, and a slightly flared open-end portion generally designated 5.

During manufacture of the device, and, specifically during the bulbing or enveloping operation an electrode mount structure generally designated 6 is inserted in the cylindrical body portion 3 of the bulb 2.

The mount structure 6 includes a plurality of mutuall spaced electrodes supported by and between a spaced pair of insulators 7. The insulators 7 may be formed of mica and include radially extending points or snubber portions 8 adapted for causing a snug fit or interference between 'the insulator and the inner wall of the envelope 2 when stem member 9 by being secured, asv by welding, to portions of conductive leads generally designated 10, which extend through the stem 9 in a suitably sealed manner and are adapted for providing electrical connections between circuits external of the tube and the various electrode elements of the tube mount. The stem 9 is formed of a suitable insulative material, such asglass, to provide a substantially solid disk and, ina manner to be described hereinafter, is adapted for being sealed to the open. end of the bulb 2 for completing the structure whereby the electrode mount is enveloped. The stem fills-formed to include a raised planar central portion 9a and an annular 'rib 9b which cooperate to provide an annular shoulder or step 9c. The purposefor this construction will be brought out in detail hereinafter. The stem 9 also includes fillets'll formed in a conventional manner about the leads 10 on the inner surface of the stem.

The flare 5 on the open end of the bulb is such that it providesan internal surface greater in diameter than the diameter defined by the points 8 on the insulators 7. Thus, when the mount 5 is inserted into the cylindrical portion of the envelope during the start of the bulbing operation, the points 8 contact the inner surface of the .bulb and are guided into the bulb on an inclined plane.

Thus, bending forces on the point 8 resulting during insertion of the mount into the bulb increase only gradually as the insertion is carried out. This results in the I points 8 bending in a manner illustrated in Figure 2 and ing of the points whereby the tight fit of the mountin the bulb would be adversely affected.

Thus, the flare 5 avoids breaking of the mica points and the various undesired effects thereof. Additionally,

it will be; seen from the foregoing description that this 3. is accomplished without reliance upon a polishing operation which without the flare would undesirably reduce the diameter of the open end of the bulb.

Following insertion of the mount in the tube bulb in the'm'anner" described'above, the stem 9'is moved down into the position shown in Figure 2 wherein the outer edgefofthe portion 921 or the upper edge of the step 90 of the stem makes peripheral contact with the internal surface'ofth'e flared'portion of the bulb. Desirably, the angleof flare of the portion 5' is such that the step 9c is received'in and makes contact with the surface portion oftthe"flare' 5 -interiorly of a median portion of the envelope wall as shown by the dot and dash line, Figure 2} With the bulb and stem in these relative positions, heat is applied thereto, as by the application of a pluralityJof circumferentially arrayed pin fires, two of which are'indicatedat 12. Thus, the contiguous portions of the bulb'andstem are softened to a consistency whereat they are adapted for flowing and fusing to provide a desired'seal between the stem and bulb.

With the 'stem'9 and flared portion 5 of the bulb heated t'othe just-described consistency, a force is applied to thestemas bymeans of an applicator illustrated in outline in Figure 3 and generally designated 13. Thus, the "stem-is movedinwardly toward the envelope for causing a fusion thereof and a mushing out or outward and up- "ward flowof the excess glass of the bulb edge into the step 90 of the stem in the mannerindicated at 14 in Figure 3. This desired flow of the excess bulb glass is facilitated by the flare of the end of the bulb and the cooperation thereof with the edge of the portion 9a when the-bulb and stem are moved toward each other. This type of seal might be described as a combination lapbutt seal since it is characterized by a butt seal between a portioniof the'flared end of the bulb and the edge of the-"portion 9a of the stem as well as a lap seal about the step 9c ofthe stem. Thus, some of the desirable attributes of both lap and butt seals are obtained. In this manner, sealing'of the stem to the bulb is effected with a' desired smoothly rounded or large-radius fillet in the sealing area and generally indicated at 15. Additionally,

the described sealing operation avoids undesired flow of the excess material 14 inwardly toward the fillets 11 formed about the leads 10.

The rounded fillet 15 and the absence of sealing material interconnecting the lead fillets 11 and the sealing region insures a high-strength seal and adapts the seal for better withstanding thermoshocking, for testing the seal and which generally involves holding the device in 100 C. water for approximately 15 seconds and then dropping it into ice water for 5 seconds.

For purposes of enhancing the appearance of the device and improving the quality of the seal obtained in 'theju'st-described manner, we distribute the excess material 14 over the lateral surface of the stem 9. To this end and while the excess material 14 is in the softened condition, the tube envelope is rolled between a pair of counter rotating elements 16, in the manner illustrated in Figure 4. As also illustrated in Figure 4, the rolling operation distributes the excess material 14 by causing it to flow upwardly'over the lateral surface of the stem and toward the outer side of the stem. Thus, we enhance the appearance of the sealed portion of the device and improve the seal while preserving the desired internal round fillet 15.

InFigure 5 is illustrated a modified form of the present invention. In this form there is provided a stem 17 comprising a disk-like member which may be formed of the same material as the stem 9 described above but which need not include the portions 9a9c described 4.v in the relative positions shown in Figure 5 whereby fu- 'sion occurs and'e'xcess bulb material is caused to flow around the lateral portions of the stem member thereby to effect a lap-seal and a desired smoothly rounded or largeradius fillet similar to that designated 15 in Figure 3. Subsequently, the seal may be rolleddesirably to distribute the excess material about the lateral portions of the stem while preserving the desired internal fillet in the manner illustrated in Figure 4.

It will be seen from the foregoing that the provision of the bulb structure including the flared open end precludes the necessity of reliance upon a fire-polishing operationto insure against breakage ofmica points, reduces cost of production, expedites the bulbing operation and minimizes conditions tending to cause presence of loose mica particles in the bulb structure. By minimizing the presence of loose micaparticles in the structure mount finished tube shrinkage or production loss dueto such particles is minimized. Additionally, avoidance of breakage of the mica points enables such points to fulfill their intended purpose of providing a tight fit of the mount in the tube bulb thereby to minimize microphonics and other undesirable eflects resulting from a loose fit. Furthermore, the seal provided as described above is adapted for reducing sealing failures by withstanding the thermoshock test to which many tubes are customarily subjected duringthe exhaust-operation following the sealing operation.

While we have shown and described a specific embodiment of our invention we do not desire our invention to be limited to the particular form shown and described, and .we intend by the appended claims to cover all modifications within the spirit and scope of our invention.

What we claim as newand desire to secure by Letters Patent of the United States is:

l. Themethod of sealing a closuremember in the open end of a glass bulb comprising the steps of preforming the open end of said bulb to provide a flare, thereafter partially inserting said closure member in saidflared open end of-said bulb and only line contacting the internal flared surface of said open end of said bulb with said closure member at a line of contact inwardly of the edge of said bulb, then heating said flared end and. closure member foreffeeting fusion thereof at the line of contact, and causing lateraly outward flow of excess flowing material over the, lateral external surface portion of saidclosure member by applying a longitudinally directed externally applied force between said bulb and closure member.

2. The method of sealing a closure member in the open end of a glass bulb comprising'thesteps of preforming the open end ofsaid bulb, thereafter partially inserting said closure member in said flared open end of said bulb and only line contacting the internal flared surface of said open end ofv said bulb with said closure member at a line of contactsdisposed inwardly of-said'open end of said bulb, then heating said flared end and closure member for effecting. fusion thereof at the line of contact, causing outward flow of excess flowing material over the lateral external surface portion of saidclosu'remember by applying. a longitudinally directed externally applied force between said bulb and-closure-member, and distributing the major portion ofexcess flowing material smoothly over theiexternal surface of said closure member by rolling the resultantfused seal.

References Cited in thefile of this patent UNITED'STATES PATENTS 2,089,044 'Thomas Aug. 3, 1937 2,171,226 'Schoonenberg Aug. 29, 1939 2,296,579 Seelen Sept. 22, 1942 2,572,055 Saldarini Oct. 23, 1951 2,513,553 Doran Oct. 30, 1951 2,581,945 Doran' Jan. 8, 1952 FOREIGN PATENTS 716 4;17'3' Germany ..a.. June 15, 1953 

